Electromagnetic friction device



Nov, 20, 1934. A, P. WARNER ELECTROMAGNETIG FRICTION DEVICE Filed March 3, 1930 Patented Nov. 2o, 1934 A 1,981,208 ELEcTRoMAcNETro FmcTroN DEVICE Arthur P, warner. Beloit, wis.; .assigner to Warner Electric Brake Corporation,

South Beloit, Ill., a corporation of Illinois Application March 3, 1930, Serial No. 432,655 l 10 Claims; (Cl. 18s- 140) This invention relates to electromagnetic friction devices and more particularly -to those having annular magnetic elements arranged for relative rotation. t

The primary object o f the invention is to provide a novel means for. efiectually dissipating the residual magnetismV which persists in magnetic structures of the above character and produces objectionable gripping engagement between their 10. coacting faces after the energizing current h as l been interrupted.

lIn carrying out this object, I p rovide a body of non-magnetic medium which is presented momentarilytojsuccessive sections of the magnet pole face automatically as an incident to' relative rotation between the magnet Vand its armature and which Aprovides an opening of such magnitude that the residual magnetic flux ineach section of the magnetwith which the body is associ'ated will be dissipated.

The linvention also resides in the novel character and location of the non-magnetic body above referred to.

Other objects and advantages of the invention will become apparent from the following detailed description taken in connection with the accomf panying drawing, in which Figure 1 is a diametrical sectional view of an Y electric brake having yan electromagnetic friction device embodying the features of theA present in vention.

Fig. 2 -is a fragmentary sectional view taken substantially along the line 2-2 of Fig. 1.

Fig. 3 is a face view of the armature ofthe fric-I tion device.

Fig. 4 is a fragmentary elevational view of a portion of th'e magnet and its armature.

4,Whilethe invention is susceptible of various In the present'instance, the non-rotatable friction lsurface of the' brake isof the band type com-f, prising a metal strip 13 encircling an inwardly projecting ange 1 4'on the anchor plate and carrying segments 15 of'friction material. Fittings go 16 are secured .to the opposite ends of the strip 1 3 and drawn by a spring 17 into abutting engagement with the opposite end surfaces of a stop 18 rigid with the anchor plate.

'I'he electromagnetic operator in. whichthe 351 I present linvention is embodied is utilized to spread ring 22 and arms 25.

4The ring 20 constitutes a magnetic core and is modifications and alternative lconstructions, I1

have shown in the drawing and will herein describe in detail the preferred embodiment, .but itv is to be understood that I do not thereby intend to limitthe invention to the specific forml disclosed but aim to cover all modifications and alternative constructions falling within .the spirit and scope oi the invention as expressed in the appended claims.

In this exemplary form, the invention is embodied .in an electric brake for avehicle wheel 5l the ends .of the band apart and thereby set the brake.- It comprises two rings 19 and 20 of magnetic material arranged concentric with the drum andadapted" for axial gripping engagement. 70 Preferably, the ring 19, which constitutes the magnetic armature, is.substantially` flat and of solid r metal construction, being oatingly supported from the drum so as to rotate'therewith and at the same time adapted for some degree of axial 75 movement. IoV this end, the back ofthering is secured at annularly spaced points to the ends' of flexible metal strips 21 which extend in a' substantially tangential direction-and are rigid at their' other ends with a ring 22 in turn riveted to n 21, it will be` observed,l act. in tension to prevent7 relative rotation between the rings 19'and 22 in 90 :one direction. Relative rotation in the other direction is prevented by engagement between the U-shaped in cross section` with a winding 26 disposed between and enclosed by its two concentric poles 27 and adapted to be energized from a storage batteryorother source of electrical power. Plates. 28 of non-magnetic material are .mounted between the poles-and provide a wear resisting surface substantially flush with the4 end faces of the 'poles and adapted to sustain the axial pressure between Vthe two magnetic rings. The magnet ring-is-supported by a circular flange portion 29 of the .anchor plate for oscillation about the axis.

,'Projecting rigidly from the outer 'magnet pole are two actuating lugs 30 having ODPOSitely facing surfaces positioned to abut against lugs 31 which are rigid with the ttings 16 on the brake band.

Upon movement of the magnet in either direction 110 I 3) one or the other f the lugs 30 will move its end -of thefbrake away from the stop 18', thereby expanding the band and its -entire friction surface against the drum.

' Suchactuation of the band-takes'place whenever the winding 26 is energised with the wheell in motion. This produces a magnetic iiux' of high intensity in the closed magnetic circuit which en-f circles the winding through the opposite sections of the magnet core and armature. The resulting magnetic attraction causes grippingngagement between the -friction surfaces 4of the two rings proportionaltothestrengthoftheenergizingcur.- rent, whereupon the magnet ring. will be driven frictionally by the amature ring thereby moving with the wheel a short amular distance. In'this circumferential movement, one end of the band is, .moved away from the stop iii which expands the band thereby pressing thesegments -15 against the-drum surface. After the normal clearance has been taken up, movement of thef magnet ceases causing slippage between the ring surfacesin the continued rotation of the wheel. 1 When the current flow is interrupted, the spring 17 acting through the medium of the fitting 16 and the lug 30 serves to restore the magnet as well e actuated end of the band to normar brake- Inasmuch as the friction faces of the rings 19 and 210 are always maintained in light'xnechanical contact by the springs 24 while the winding -26--is deenergined, it is imn a 1 for'the magnetic ilux produced by the initial energization of the winding to overcome a'n air gap between the As a` result, the attractive force and. thereforathedegreeofbraklngactionis always .directly proportional to the strength of the ener` sizing current.

A magnet of the m'eure.8uchapersistentdrag,ifallowedto wouldbeparticularlydetrimentalinabrake the above character not only because of waonwnanumontne butbecause itl subiecta the magnetic ele- 'groove or depression 33 formed in the friction thereto-intravelling around the annular face derst revolution f relative rotation' between the l l 1,981,208 f away from normal brake-released position (Fig. For the sake of simplicity of structure, air-is.

employed herein as the non-magnetic medium and the body 32 thereof which is exposed to the magnet face is dened by a radially extending face of the armature ring and preferably extending transversely across the entire. face ofthe magnet. In order to retain the rugged character of the armature ring, the groove is formed withoutinterrupting the continuity of the ring as by depressing a segmental section 34 of the ring away from its friction face.

The face ofthe armaturel thus constructed presents to the face of the magnet a hat magneticfsection occupying substantially the entire `ring circumference and a relatively shorter nonmagnetic segment which travels laround and is presented momentarily to successive segmental sections of the pole faces in each revolution of the armature ring. Inasmuch as the non-magnetic section. of the armature face is exposed to both poles of the magnet, the magnet circuit through any section of the magnet core opposite the air gap is eifectually broken 'even though the vgroove deiining the magnetic medium lill.

is relatively shallow. l

g The action of the revolving air gap in dissipat-- ing lthe residual magnetic field may be best un, derstood by considering the'magnet core as being compod of a multiplicity of short segments ar- 1w Obviously, the presentment of the air gap 32 momentarily to any one of these segments will cause the residual iiux in such segment to be dissipated because. the density of such iiuxis not sumcient no to overcome the high reluctance whichthe gap interposes in theV magnetic circuit through the segment. In a similar way, the' residual iiux lin each segment is destroyed as the gap is presented4 115 ned by all of the segments. Thus the total re sidual .iield andtherefore the attractivel force produced thereby will decrease gradually in the ,ranged side by side to form the complete annulus.

magnet and the armature following deenergzation of the winding 26. The magnet will become completely demagnetiaed in the present instance l at the completion of the revolution of the vehicle wheelinasmuch asthefaceofthearmature ring 4 carries onlyoneairgap 32. t

The eifectiveness of anon-magnetic body operating as above describedl is determined not only by its non-magnetic property andthe structural characteristics ofthe magnetbut by its magnitude, particularly its lengthmeasured along'acirm cumference of the magnet ring. For example, with an air gap of very short'circumferential lengththeresidualiiuxinthemagnetsection exposedy tosuh a gap atanaaivcn "01M stray throughthearmature by'leaking diagonally u acrosstbeedgeportionsofthegapwhichareof lower reluctance. Thus the magnetic circuit one groove which, of course, necessitates a com.

'plete revolution .of the armature in order to combetween the friction elements. The rate of rela' tive motion .between the elements determines the time during which any given pole area is exposed to the non-magnetic medium. Therefore;l owing to the inherent time lag involved in the complete dissipation of a magnetic flux, it will be apparent that a gap of a length sufficient to dissipate 'the residual flux when the -coacting elements are ro- .tating at a very `low speed might not eifectually eliminate the field when the rotation isat a com'- paratively higher speed. Therefore, the length of the gap shouldbe increased toja point where the residual flux will disappear under the speed of relative'rotation to be encountered in the lservice to which the device is put.

In view of the-many influential factors involved, the determination of the mostadvantageous-length of the non-magnetic armature'section for any magnet structure will be a matter of experimentation. The results of experiments i with magnetic friction devices of the character.

and in the environment vabove described show that the-l residual field produced upon deenergiz'ation.of lthe winding 26 can be effectually .dissip pated when the circumferential length of the non-magnetic medium is approximately twice the .radial width of the magnet face.

The thickness ofthe air gap as measured in anl axial direction need becconsidered only' when the entire gap is defined by a magnetic medium as is done in the present case. Thus the groove 33 'should beof-a depth such as to prevent'the re- The radial width of the non-magnetic mediuml is not an important factor to be considered in the present instance because the groove 33 ex' tends radially across the entire fa'ce of the armature. In case only one pole of the magnet is exposed to the gap orboth poles exposedwithout interrupting the continuity ofthe armature surface opposite the wear plates 28, the gap should be wider than the' exposed pole face or faces'by an amount sufficient to prevent leakage oi' the residual flux i'n a radial direction to the adjacent portion of thefarmature. t

Also, the annular poles of the magnet might be spaced so close to each other that the intervening gap wouldfnotprevent leakage of the residual ,flux directly from one pole to the other,

condition is not encountered in the presentin-I stance owing to thesubStantlal radial width of.

v the non-magnetic wear plates 28 which separate the poles 27..

'From the foregoing it will be' napparent;- that an effective means has been -provided for eliminating the ldetrimental action of residual magnetism in an electromagnetic friction device f' the class described. This'result is attained'without increasing the reluctance of the magnetic cir'- cuit through the magnetl core sections and the amature and with only a relatively small decrease 4in the total attractive f orce which the magnetwould otherwise be capable of producing. By utilizing aixas then'on-magnetic medium and preserving the continuity of the ,armature ring,.

cated nor its strength reduced. The residual flux eliminating means is particularly adapted for use in theV environment above described Where the magnetic circuit through the coacting friction elements is intentionally maintained closed after the energizing currenthas been interrupted. Inasmuch as complete dissipation of the residual magnetism is effected by a non-magnetic body carried by'only one of the magnetic rings and the iron surface of the other ring is therefore' .bridging said pole faces, a winding enclosed by said poles and adapted when energized to bringl the coacting lfriction faces of said rings into gripping engagement, said rings being arranged for relative rotational movement, Iand means operating as an incident to relative rotationaly movement between said rings to dissipate the -residual magnetic field-which threads the magnetic circuit through said rings 'upon'deenergizaf tion of said winding comprising avgroovel formedl in and extending radially across the entire face of said second ring so asv to define an air gap opposite both4 of said pol faces, the edges oi. said groove being spaced circumferentially a substantial 'distance so as to allow dissipation of the residual flux in each section of said magnet ring with which said air gap becomes associated in the relative motion 'between the rings.

2. An electromagnetic friction device combining a magnet ring having a .flat annular friction face with two concentric pole faces substantially flush therewith, a flat ring of magnetic material constituting an armature for said magnet 'and 4havinga friction face adapted to be brought into gripping engagement with the face of said magnet upon energ'ization of the. latter,'said rings being arranged for relative rotation, and anair gap interrupting-the continuity of the armature face and defined by a radially extending groove formed by depressing a segment 'of said armature ring, saidair gap being presented to successive sections of the magnet face as an incident t relative rotation between the rings. v

3. An electromagnetic friction device combining an annular magnet having two continuous pole faces, an armature for said magnet having faces and adapted to be brought into frictional gripping engagement with lthe face of said inaga face coacting with and overlapping said pole net upon energization of thelatter, and a body of air interrupting the continuityy of said armature face opposite a segmental portion of one of said4 pole faces, said body being presented tosuccessive sections 'of thepole face as an incident to relative rotation between said rings whereby to, open the magnetic'circuits throughsuch sections presenting a face' to said pole faces having two segmental sections one of which is composedof magnetic material coacts with substantially the ,entire area .ofviiaid pole faces, the' other section bei'ri'g'fc'omposed of a nonmagnetic medium and acting in the relative rotation between saidrings following deenergization of saidwinding to interrupt the magnetl circuit througheach cir-.

Icumferential section of said ilrst ring whereby to dissipate the residua'lmagneticux threading v such sections.

5. Anr electromagnetic frictionr device combining an annular magnet having a pole face`and an annular armature adapted to be brought into ygripping engagement with the face of said mag-4 net upon energi'zation of the latter, there being a nongmagnetic body exposed to thei magnet face over a\ substantial circumferential length thereof and adapted to be wiped around the entire face ofi-'the magnet as` an incident to one revolu- .curent in said magnet. .s 8. An electromagnetic friction device combining a magnet ring providing two spaced poles with tion` of 'relative rotational movement between said magnet and said amature whereby to interrupt the magnetic iiux circuitthroughsuccessive sections of said magnet and thereby dissipate the residual magnetic ilux which threads such circuits upon interruption of the energizing continuous circular iron faces, and an annular winding disposed between said poles, a second ring of 'magnetic material adapted to be brought into irictional grippingv engagement with said iirst ring and overlying said poles, there being a single body L of non-magnetic medium interrupting the continuity of the surface of said second ring opposite at least one of said poles providing, in'the iri'ag` 'netic `circuit through the section .of the ring with which it is associated at anytime, 'a reluctance of suiilcient width and circumferential length t0 elect dlipation 0f the inagnetic deld during relativerotation between the v'rings through one complete revolution. y

7. An electromagnetic friction device combininga pair of annular magnetic'elements arranged for relative rotation and adapted to be brought. yinto frictional gripping engagement by eniergua-` tion ofawinding carried by onecf the elements,

interrupting and abodyofnon-magneticmedium. Ythilironsurfaceuftheotherelesnentaluiaeting' as an incident to a single complete revolution of relative rotationbetween the elementsto 'comm di'lipation-of the residual nunmngininerinnroiiowing oruiewinaing.

8. An electromagnetic friction device combiningan annular magnetic winding and apaii.of` magnetic rings enclosing said winding and arranged for relative rotational movement-by slippage at their engaging friction faces, the reluctance of the magnetic circuit through said rings being constant for all angular positions'ofthe i' rings relative to each other, and a body of nonconstant during relative rotation between the 4rings when said winding is energized. there being a non-magnetic body interrupting .a segmental section of said magnetic circuit and acting during relative motion -between the rings after de'- lil! y no of its gripping faire oppo. 120%" v polef soasto providean opening in said' -circuitthrouh the ofnimeient magnitudeto allow complete de-l i nvwaamf 

